Miguel Mitrofanov wrote:
There's a third way, too, and I haven't seen anybody mention it yet
I've noticed it, but there are some problems with this representation,
so I decided not to mention it. It's OK as far as we don't want
functions working on two areas - I don't see, how we can implement, say,
intersect :: Shape -> Shape -> Bool in this way. However, it's a useful
pattern.
The problem is no better or worse for this third way than for type classes.
class Shape a where {
intersect :: Shape b => a -> b -> Bool
}
data Shape a = { intersect :: Shape b => a -> b -> Bool }
in fact, the syntax is rather similar, too! :)
Jules
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